Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Reevaluate Everything - Apparently Things Need Fixing

Originally Posted by 3DD

Oh yeah. The house is about 1700, with a room above the garage, and this room pretty much gets the sun all day. The A/C takes about 3+ hrs to cool the house from 85 to 80 on 95 degrees days, which I think is too long, and on the 95+ days, the A/C can't seem to the temp low enough so it's always on.

Edit: wrote response as
So the compressor is Rated 40,000.

The house is a moderate 1700-sf.

The unit runs all the time at 95-F OAT.That does NOT mean that, if 95-OAT were the summer design, that the system is delivering its supposed nominal 3.5-nominal tons of cooling, or that the system is delivering what a load calc would say!

First, I am willing to bet there are some things keeping that system from delivering its nominal tonnage rating. Be sure that the duct system is thoroughly analyzed, & if not up to specs, brought to specs.

Second, as shophound has hounded on elsewhere, the home needs to be examined & Energy Conservation updated. The entire home conditions & the HVAC system are an inseparable integrated system.

You might end up with a 2.5-ton system doing the job. The Rated around 4-ton system may only be delivering 2 or 2.5-ton of cooling, in a home that needs Energy Consumption fixes over the garage..(?)

Run a psychrometric on the required data, so you know what the system is actually delivering at those conditions.

Edit: Well, just rambling now. - Darrell

Last edited by udarrell; 08-08-2008 at 04:20 PM.
Reason: A Post while I was typing - 40,000-btuh compressor

The unit runs all the time at 95-F OAT.That does NOT mean that, if 95-OAT were the summer design, that the system is delivering its supposed nominal 3.5-nominal tons of cooling, or that the system is delivering what a load calc would say!

First, I am willing to bet there are some things keeping that system from delivering its nominal tonnage rating. Be sure that the duct system is thoroughly analyzed, & if not up to specs, brought to specs.

Second, as shophound has hounded on elsewhere, the home needs to be examined & Energy Conservation updated. The entire home conditions & the HVAC system are an inseparable integrated system.

You might end up with a 2.5-ton system doing the job. The Rated around 4-ton system may only be delivering 2 or 2.5-ton of cooling, in a home that needs Energy Consumption fixes over the garage..(?)

Run a psychrometric on the required data, so you know what the system is actually delivering at those conditions.

I really appreciate all you experts helping out on this, even the dangling wrangler. It's just that the more A/C guys I got, the more confused I get. The unit is over 15 years old, so I do want to get it replaced.

I really appreciate all you experts helping out on this, even the dangling wrangler. It's just that the more A/C guys I got, the more confused I get. The unit is over 15 years old, so I do want to get it replaced.

Thats why its better to do a load calc. Instead of just replacing with what is already there.
Then you can see what areas of your home you may be able to make improvements to. To decrease the size A/C you need, and save money both on equipment cost, and operating cost.